"I'm not Rain Man"

I wrote this update on Facebook the other day, under the banner "Sh*t my wife says".  It got more "Likes" and comments from family than my usual witty banter.  Any thoughts as to why?
Wife: "Let's see... 170 square meters, $16/square... Alain, what's 170 times 16?"
Me: "Wtf? I'm just supposed to know that off the top of my head? I'm not Rain Man!"
Wife: "Come on!" *snaps fingers*
Me: "Okay, um, 2560".
Wife: "See, that wasn't that hard!"